18 BULLETIN OF THE BUREAU OF FISHERIES 



of the progressive and regressive strokes. At present we have no means to measure 

 the absolute velocity of the motion of the cilium, but Kraft (1890) has estimated 

 that the velocity of the progressive phase is five or six times greater than that of the 

 regressive period. This means that the work performed during the forward motion 

 is one hundred and twenty five or two hundred and sixteen times greater than that 

 produced during its backward movement. It is obvious that even an insignificant 

 decrease in the ratio between the velocities of the two strokes will result in a con- 

 siderable loss of efficiency of the ciliary motion. 



The coordination of the ciliary activity is another factor that determines the 

 constancy of the current produced by the gill epithelium. The maintenance of a 

 constant pressure inside the gill cavity depends on a definite rhythm of strokes along 

 all the filaments of tlie gill. As soon as the rhythmic motion in some of them becomes 

 irregular a leakage occurs through the wall of the gill, resulting in a drop of pressure 

 and in retarding or complete stoppage of current. In this manner even small dis- 

 turbances in the rhythm of the beats of lateral cilia along one or several filaments 

 result in considerable fluctuation in the velocity of the outgoing current. The vari- 

 ations in the velocity of the current that occur both below 15° C. and above 25° 

 should be attributed to the disturbances in the rhythm of beats. Observations made 

 by the author on the excised pieces of the epithelium kept at temperatures ranging 

 from 5° to 15° show that the irregularity in the rhythm of the ciliary motion becomes 

 noticeable under the microscope as soon as the temperature drops to 15°. At 10° 

 the characteristic metachronial wave often is interrupted because the cilia in some of 

 the filaments begin to beat simultaneously instead of in succession, as they do nor- 

 mally. The result is that in certain blocks of the filament all the lateral cilia beat 

 simultaneously at the same phase, while in the other portions of the filament the 

 metachronial rhythm is maintained. At 5° the cihary motion becomes slow and 

 irregular. Because of the lack of coordination at this temperature no current is 

 produced, although the cilia are beating. 



The results of present experiments on the effect of temperature bn the rate of 

 flow of water through the gills parallel the data obtained by Gray (1924) on Mytilus. 

 Gray's method consisted in determining the relative speed of the cilia by recording 

 the time required to move at a imiform rate a small circular plate of platinum over a 

 distance of 1 centimeter along the surface of the gill. It should be borne in mind, 

 however, that the transport of a particle over the ciliated surface is accomplished by 

 the frontal cilia, while the current running through the gills is produced by the 

 lateral ciUa. As in the case of the oyster, the activity of the frontal cilia of Mytilus 

 is a function of temperature. Gray finds that between 0° and 33° the speed of the 

 cilia increases with the rise in temperature, although the amphtude remains normal. 

 Between 34° and 40° a marked falling off in the amplitude of the beat occurs, fol- 

 lowed by the reduction of the rate of beat. Experimenting with oysters, I was unable 

 to observe the changes in the amplitude of the beats, and the attempts to apply 

 Gray's method for measuring the mechanical activity of the frontal cilia were unsuc- 

 cessful. The gills of the oyster contain numerous mucus glands that are stimulated 

 by contact with metal and secrete mucus, which accumulates on the surface of the 

 gill and increases the resistance to the motion of the plate. On the other hand, 

 repeated mechanic3,l stimulation of the ciUa by contact with metal causes a complete 



